The present invention relates in the first place to a coloured polyester container obtained in a two-stage method in which, in a first stage, starting from polyester granular material, injection moulding is used to produce a coloured preform which is converted to the desired final shape in a second stage.
The production of coloured containers from polyester is known. In this connection, a holder is understood to mean any product which is capable of containing a quantity of liquid, semisolid or solid product and may be formed by a bottle, a beaker, a tank, a dish, etc.
In producing a coloured container from polyester, for example, a coloured bottle from polyester, a two-stage method is employed in which, in the first place, a coloured preform is produced which is converted to the desired final shape in a second stage by blowing. This manner of working provides the possibility of allowing the manufacture of the preform and the conversion to the final shape in the second stage to take place at different places. The preform is, for example, produced centrally in a plastic material processing industry; the standard preforms are then transported to the various customers who have installations for converting the polyester work piece by means of an enveloping mould into the final shape. Such a manner of working entails appreciable savings in the transport costs and is therefore frequently used. To produce a coloured container from polyester, the possibility is known of starting from colourless polyester granular material which, prior to being introduced into the injection moulding machine, is mixed with a product which contains a dyestuff and/or pigment and which is added in a quantity such that the desired colour concentration in the polyester is reached. The coloured product may, for example, consist of a homogeneous coloured polyester granular material which contains, for example, 10% dyestuff and/or pigment or a paste consisting of dyestuff and/or pigment and a viscous liquid, for example, glycerol.
A coloured polyester container which is obtained in the known manner described above has, however, the disadvantage that, starting from coloured polyester granular material as an additive, there is a restriction on the colour density range, while it is difficult to achieve a good colour homogeneity at high colour density. If a coloured paste is used, there is the disadvantage that, as a result of the incorporation of a liquid carrier in the polyester, a deterioration of mechanical properties of the polyester is observed, as a result of which the possible applications decline in number; moreover, the possibility exists that the liquid carrier used is leached out of the holder during use, which is undesirable for, for example, use with foodstuffs.
The object of the present invention is to provide a coloured polyester container which has a homogeneous colouring, which can be produced in a colour density between wide limits, the mechanical properties of which do not differ, or virtually do not differ, from those of a colourless container and in which the ability of any agents used to be leached out is minimumal.